1. Field of the Invention
The present invention relates to a portable terminal and a portable terminal communication method for performing communications while minimizing deterioration of the communication quality even in a case where a radio wave environment is in a deadlock.
2. Related Art
There are mobile telephones including a plurality of antennas so as to have the diversity effect.
A base station transmits radio waves in a service area, and forms a call channel between it and a mobile telephone by using the radio waves. The radio waves transmitted from the base station have strong directivity, so the receiving condition in the mobile telephone may fluctuate depending on the arriving direction of the radio waves.
On the other hand, when explaining a mobile telephone, a mobile telephone is formed in an elongated shape which is conveniently portable, so that a user can easily hold it with one hand. In a mobile telephone, a receiver is built in at one end of the elongated phone body, and an antenna is incorporated in the other end on the opposite side. This arrangement is defined so as to prevent radio waves transmitted/received from/by the antenna from affecting bad influence on the user for example.
In view of the characteristics of a mobile telephone described above, a part of the antenna incorporated in the mobile telephone is covered with a hand of the user (derivative) when he/she takes a position of calling or creating an e-mail or the like, whereby the antenna characteristics are changed.
As described above, when the antenna incorporated in the mobile telephone is covered with a hand of the user, or when the direction of the antenna incorporated in the mobile telephone is inappropriate with respect to the arriving direction of radio waves from the base station, the receiving characteristics of the antenna are deteriorated. In such a case, if the arriving direction of radio waves from the base station is only the deteriorated direction, the incoming call rate may be deteriorated significantly.
Conventionally, in order to prevent the incoming call rate in a mobile telephone from being deteriorated even in a case where the arriving direction of radio waves from the base station is only the deteriorated direction, a sub antenna is provided with a function same as that of the main antenna so as to be switched to one having a better receiving level (see, for example, Japanese Patent Application Laid-Open No. 2002-135023 and Japanese Patent Application Laid-Open No. 2003-264417).
In the method adopted conventionally as described above, a sub antenna is required to have a function same as that of the main antenna. Therefore, the number of components built in a mobile telephone increases. Along with it, the weight of the mobile telephone becomes heavier, and a mounting space required for mounting the components within the mobile telephone must be increased. This means a certain sacrifice must be made in the characteristics of a mobile telephone, so there has been a problem that a negative element is caused to the merchantability of a mobile telephone.